Summary A Helicopter Transport Services Bell205 helicopter, C-FPAZ, serial number30016, was on contract to the Province of Saskatchewan's forest fire suppression program. At approximately 2000 central standard time, the provincial fire coordinator requested the pilot of C-FPAZ to resume water bucketing on a small fire approximately five miles east of Chitek Lake, Saskatchewan. While manoeuvring to the drop point, at less than 40knots and approximately 150feet, the pilot saw the reflection of a yellow caution light in the door window and heard an associated low-rotor-rpm warning. The corresponding N2 (mainrotorrpm) indication was 97to 98percent. The pilot released the water load and reduced the torque. The rotor rpm did not recover and the pilot prepared to make a forced landing. He kept power on until the bucket was clear of the trees below and then reduced collective in an attempt to regain rotor rpm. There was no resultant rotor rpm increase and the helicopter descended rapidly over a short distance, struck an earthen brush pile, and rolled onto its side. The accident occurred during daylight hours at 2010. The pilot of another helicopter saw C-FPAZ go down, called the Chitek Lake Fire Base for emergency medical personnel, then landed adjacent to the crash site. The pilot of C-FPAZ was walking unsteadily away from the aircraft, and there were flames emanating from the exhaust stack. The engine was still running. Neither pilot attempted to extinguish the flames. The engine stopped several minutes after the two pilots exited the crash site. On receipt of the second helicopter's call, the fire coordinator at the Chitek Lake Fire Base dispatched emergency medical personnel and a water bomber aircraft to the site. The accident pilot, who had sustained serious injuries, was stabilized and evacuated to Saskatoon. The water bomber dropped water and retardant on the area immediately surrounding the crash site. Ce rapport est galement disponible en franais. Other Factual Information The pilot held a valid Canadian commercial helicopter pilot licence, which was endorsed for several helicopter types, including the Bell205. Available information indicated that the pilot was adequately rested, in accordance with company and Transport Canada requirements, on the day of the accident. The observed weather at 2000 central standard time1 at the Vimy Fire Base, approximately five miles from the accident site, was as follows: temperature at 28C, with light winds out of the south. On 08 July 2002, three days prior to the accident, a grease seal on the forward main input drive shaft coupling of the helicopter had failed. The failure was detected during a daily inspection, after the helicopter had operated for 6.1hours. The grease seal was replaced and installed with Bell204 grease, as recommended by the Bell205 Component Repair and Overhaul manual. As part of the seal replacement procedure, the aircraft maintenance engineer (AME), disassembled, cleaned, and inspected the splined components of the forward coupling on the drive shaft. This inspection did not reveal any indication of wear or overheating of the splined components. The aft coupling assembly for the drive shaft was not disassembled. Temperature-sensing temp-plates, installed on the outside of both coupling assemblies, were inspected and did not show that either coupling had experienced an over-temperature condition. Although the AME completed his work report and appropriate tag entries for the replacement of the forward coupling grease boot, there was no certification statement entered in the helicopter journey log for the accomplished work. On 10 July 2002, C-FPAZ was returned to service and was engaged in fire-suppression operations, which involved several water bucketing trips and two crew moves. There were no reported abnormal vibrations or engine indications, with the exception of a slight main rotor rpm loss (droop) during the water pickups. Because of the high ambient temperatures, this was not considered abnormal by the pilot. A daily inspection was completed following that day's flying activities, during which the drive shaft couplings and temp plates were inspected with no apparent grease leakage or overheating of either coupling being detected. On the day of the occurrence, C-FPAZ was again dispatched on fire-suppression operations, which initially involved a crew move, followed by approximately six hours of water bucketing and another crew move. During the bucketing operations, the main rotor rpm drooped slightly while picking up water with the bucket. There was no reported main rotor rpm droop while manoeuvring to the water drop position, until the time of the occurrence. Examination of the wreckage and surrounding area yielded the following information: The helicopter had sustained substantial damage from deceleration forces on impact. The main rotor, tail boom, and cabin areas were bent and sheared from the resulting overload forces. Damage to the main rotor and transmission mounts was consistent with a low rpm impact with the ground and subsequent contact with the fuselage. The transmission mounting structure had been bent forward, which allowed the free-floating main input drive shaft to spin out of the forward coupling and eventually disengage from the engine and transmission. The splined end (forward transmission side) of the main input drive shaft showed extensive wear and heat damage. There was helical scoring from the drive shaft coupling teeth into the plastic-state metal of the splined drive shaft. The inside teeth of the coupling showed indications of high heat and wear, but had remained relatively intact. The corresponding teeth on the shaft were almost completely ground off. The damage to this end of the shaft was so extensive that a determination of the pre-failure condition of the shaft was not possible. Most of the rubber portion of the forward coupling grease seal was missing. Only the seal mounting hardware remained. The inner teeth of the outer coupling were filled with carbon and remnants of teeth from the drive shaft. The carbon material was subsequently tested and found to be representative of a substantial quantity of grease that had carbonised due to excessive heat. There was no indication of grease leakage in the surrounding area. The aft drive shaft coupling failed as a result of overload forces, produced when the shaft spun out of the forward coupling. The grease seal on this end was in place, and there were indications of grease spatter on the forward side of the engine compartment. The tail boom was bent and the tail rotor drive shaft coupling had separated. The water bucket was connected to C-FPAZ's cargo hook by a 60-foot long-line, cinched at the 80percent setting, which corresponded to a calculated total sling load weight of about 3060pounds. The helicopter had approximately 800pounds of fuel on board. The maximum permissible gross weight for the helicopter was 10500pounds. The estimated total weight of the aircraft and sling load at the time of the accident was 9622pounds. The electric cargo release system arming switch was in the armed position. The main input drive shaft in the Bell205 does not have a finite service life. It is maintained on an on condition basis, with a 600-hour inspection and re-grease interval. The shaft in the accident helicopter had operated for 187.4hours from the time of its last 600-hour inspection to the time of the grease seal failure on 08July2002. The shaft requires a continuous internal coating of grease to reduce frictional heat and premature wear, and the grease seals, which are inspected daily for damage and leakage, retain the grease within the shaft coupling. The recommended pilot procedure following an engine failure or loss of main rotor rpm is to execute an autorotative descent.2 Helicopters have critical flight regimes, from which the possibility of establishing a successful autorotation is extremely low.3 The Bell205 pilot flight manual limitations section specifies these conditions in its height/velocity diagram.4 The height/velocity diagram directs pilots to avoid operating under specified conditions of altitude and airspeed. However, this direction does not constitute a regulatory limitation for external load operations.5 Helicopters engaged in water bucketing (external cargo) operations routinely operate under these critical conditions.